AMG-the esteemed Mercedes-Benz brand that morphs stately cruisers into psychotic chariots-has done it again. After joining the Affalterbach lineup as the compact CLA-class, this version gets special powertrain and chassis enhancements to help create the relentless CLA45. While its insane acceleration and tenacious grip are thrilling on the racetrack, the merciless Mercedes punishes passengers on uneven tarmac, and its performance is closely matched by more merciful-riding rivals.